We always hear from the community that gravity is difficult to quantize, and quantum gravity field theories have some difficulties in terms of renormalization and are associated with quantum anomalies, such as,
A list of inconveniences between quantum mechanics and (general) relativity?
What's the key point to argue that pure gravity can't be renormalizable from two-loop?
Is there any straightforward reference which shows using explicit derivations why all these facts are true? because most of quantum field theory books lack such rigorous explanation
